systemd: add support for socket activation via systemd (#401)

dlt-daemon now support activation via systemd socket.
This allows dlt-daemon to be started as soon as an application
is requesting access to the dlt socket.
This commits implements opening the socket only when
UNIX_SOCKET is used for IPC

Signed-off-by: Alexander Mohr <alexander.m.mohr@mercedes-benz.com>

Signed-off-by: Alexander Mohr <alexander.m.mohr@mercedes-benz.com>

5 files changed, 77 insertions, 1 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 49494af..2bcad1f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -48,6 +48,7 @@ option(BUILD_SHARED_LIBS      "Set to OFF to build static libraries"
 option(WITH_SYSTEMD           "Set to ON to create unit files and systemd check on dlt-daemon startup"           OFF)
 option(WITH_SYSTEMD_WATCHDOG  "Set to ON to use the systemd watchdog in dlt-daemon"                              OFF)
 option(WITH_SYSTEMD_JOURNAL   "Set to ON to use the systemd journal in dlt-system"                               OFF)
+option(WITH_SYSTEMD_SOCKET_ACTIVATION "Set to ON to use systemd socket activation"                               OFF)
 option(WITH_DOC               "Set to ON to build documentation target"                                          OFF)
 option(WITH_MAN               "Set to ON to build man pages"                                                     OFF)
 option(WITH_CHECK_CONFIG_FILE "Set to ON to create a configure file of CheckIncludeFiles and CheckFunctionExists" OFF)
@@ -92,6 +93,7 @@ option(WITH_EXTENDED_FILTERING "Set to OFF to build without extended filtering.
 
 option(WITH_DLT_DAEMON_VSOCK_IPC "Set to ON to enable VSOCK support in daemon"                                   OFF)
 option(WITH_DLT_LIB_VSOCK_IPC    "Set to ON to enable VSOCK support in library (DLT_IPC is not used in library)" OFF)
+
 set(DLT_VSOCK_PORT "13490" CACHE STRING "VSOCK port number for logging traffic.")
 
 # RPM settings
@@ -214,7 +216,7 @@ else()
     message(STATUS "Disable network trace interface since message queue is not supported")
 endif()
 
-if(WITH_SYSTEMD OR WITH_SYSTEMD_WATCHDOG OR WITH_SYSTEMD_JOURNAL)
+if(WITH_SYSTEMD OR WITH_SYSTEMD_WATCHDOG OR WITH_SYSTEMD_JOURNAL OR WITH_SYSTEMD_SOCKET_ACTIVATION)
     find_package(PkgConfig REQUIRED)
     execute_process(COMMAND pkg-config --modversion systemd OUTPUT_VARIABLE SYSTEMD_VERSION)
     string(REPLACE "\n" "" SYSTEMD_VERSION ${SYSTEMD_VERSION})
@@ -231,6 +233,13 @@ if(WITH_SYSTEMD OR WITH_SYSTEMD_WATCHDOG OR WITH_SYSTEMD_JOURNAL)
         add_definitions(-DDLT_SYSTEMD_JOURNAL_ENABLE)
     endif()
 
+    if (WITH_SYSTEMD_SOCKET_ACTIVATION)
+        if(NOT DLT_IPC STREQUAL "UNIX_SOCKET")
+            message(FATAL_ERROR "WITH_SYSTEMD_SOCKET_ACTIVATION is only supported for UNIX_SOCKET")
+        endif()
+        add_definitions(-DDLT_SYSTEM_SOCKET_ACTIVATION_ENABLE)
+    endif()
+
     set(systemd_SRCS ${PROJECT_SOURCE_DIR}/systemd/3rdparty/sd-daemon.c)
 
     set(SYSTEMD_UNITDIR "${CMAKE_INSTALL_PREFIX}/lib/systemd/system" CACHE PATH
diff --git a/src/daemon/CMakeLists.txt b/src/daemon/CMakeLists.txt
index e4e96bd..f7aaa26 100644
--- a/src/daemon/CMakeLists.txt
+++ b/src/daemon/CMakeLists.txt
@@ -61,6 +61,9 @@ endif(WITH_UDP_CONNECTION)
 
 add_executable(dlt-daemon ${dlt_daemon_SRCS} ${systemd_SRCS})
 target_link_libraries(dlt-daemon ${RT_LIBRARY} ${SOCKET_LIBRARY} ${CMAKE_THREAD_LIBS_INIT})
+if (WITH_SYSTEMD_SOCKET_ACTIVATION)
+    target_link_libraries(dlt-daemon systemd)
+endif()
 
 install(TARGETS dlt-daemon
         RUNTIME DESTINATION bin
diff --git a/src/daemon/dlt_daemon_unix_socket.c b/src/daemon/dlt_daemon_unix_socket.c
index ea889b0..4b9f472 100644
--- a/src/daemon/dlt_daemon_unix_socket.c
+++ b/src/daemon/dlt_daemon_unix_socket.c
@@ -38,6 +38,9 @@
 #include <sys/stat.h>
 #include <syslog.h>
 #include <errno.h>
+#if DLT_SYSTEM_SOCKET_ACTIVATION_ENABLE
+#include <systemd/sd-daemon.h>
+#endif
 
 #include "dlt-daemon.h"
 #include "dlt_common.h"
@@ -91,6 +94,48 @@ int dlt_daemon_unix_socket_open(int *sock, char *sock_path, int type, int mask)
         return -1;
     }
 
+#ifdef DLT_SYSTEM_SOCKET_ACTIVATION_ENABLE
+
+    char **names = NULL;
+    const int num_fds = sd_listen_fds_with_names(0, &names);
+    bool sd_socket_open = false;
+    int i;
+
+    if (num_fds <= 0) {
+        dlt_vlog(LOG_WARNING, "unix socket: no sockets configured via systemd, error: %s\n", strerror(errno));
+    } else {
+        for (i = 0; i < num_fds; ++i) {
+            if (strcmp(sock_path, names[i]) != 0) {
+                continue;
+            }
+
+            if (sd_is_socket_unix(i + SD_LISTEN_FDS_START, type, 1, names[i], strlen(names[i])) < 0) {
+                dlt_vlog(LOG_WARNING,
+                        "unix socket: socket with matching name is not of correct type or not in listen mode, error: %s\n",
+                        strerror(errno));
+                continue;
+            }
+
+            *sock = i + SD_LISTEN_FDS_START;
+            sd_socket_open = true;
+            dlt_vlog(LOG_INFO, "unix socket: sock_path %s found systemd socket %s\n", sock_path, names[i]);
+            break;
+        }
+
+        /*
+         * The caller [of sd_listen_fds_with_names] needs to free the array
+         * itself and each of its elements with libc's free() call after use.
+         * */
+        for (i = 0; i < num_fds; ++i) {
+            free(names[i]);
+        }
+        free(names);
+    }
+
+    if (!sd_socket_open) {
+        dlt_vlog(LOG_INFO, "unix socket: sock_path %s no systemd socket found\n", sock_path);
+#endif
+
     if ((*sock = socket(AF_UNIX, type, 0)) == -1) {
         dlt_log(LOG_WARNING, "unix socket: socket() error");
         return -1;
@@ -118,6 +163,11 @@ int dlt_daemon_unix_socket_open(int *sock, char *sock_path, int type, int mask)
     /* restore permissions */
     umask(old_mask);
 
+#ifdef DLT_SYSTEM_SOCKET_ACTIVATION_ENABLE
+    } // end of: if (!sd_socket_open) {
+#endif
+
+
     return 0;
 }
 
diff --git a/systemd/CMakeLists.txt b/systemd/CMakeLists.txt
index 50e91d9..bfd4cd9 100644
--- a/systemd/CMakeLists.txt
+++ b/systemd/CMakeLists.txt
@@ -63,6 +63,12 @@ if(WITH_SYSTEMD)
         install(FILES ${PROJECT_BINARY_DIR}/systemd/dlt-adaptor-udp.service DESTINATION ${SYSTEMD_CONFIGURATIONS_FILES_DIR} )
     endif(WITH_DLT_ADAPTOR_UDP)
 
+    if (WITH_SYSTEMD_SOCKET_ACTIVATION)
+        configure_file(${PROJECT_SOURCE_DIR}/systemd/dlt.socket.cmake ${PROJECT_BINARY_DIR}/systemd/dlt.socket)
+        message( STATUS "Configured systemd socket file:dlt.socket" )
+        install(FILES ${PROJECT_BINARY_DIR}/systemd/dlt.socket DESTINATION ${SYSTEMD_CONFIGURATIONS_FILES_DIR} )
+    endif()
+
     message(STATUS "Unit files will be installed to ${SYSTEMD_CONFIGURATIONS_FILES_DIR} after make install" )
 
 endif(WITH_SYSTEMD)
diff --git a/systemd/dlt.socket.cmake b/systemd/dlt.socket.cmake
new file mode 100755
index 0000000..9764c0f
--- /dev/null
+++ b/systemd/dlt.socket.cmake
@@ -0,0 +1,8 @@
+[Socket]
+ListenStream=@DLT_USER_IPC_PATH@/dlt
+FileDescriptorName=@DLT_USER_IPC_PATH@/dlt
+SocketGroup=dlt
+SocketMode=0666
+
+[Install]
+WantedBy=sockets.target
\ No newline at end of file